Field of the Invention
The invention relates to a method of, and an apparatus for, testing liquids.
Such a method and such an apparatus are used, in particular, for monitoring liquids in clarification plants.
Until now, calorimetric test apparatuses have tested liquids. Calorimetric test apparatuses include a test vessel, a precisely weighed mixture of chemical reagents in solid or liquid form. The composition of the mixture is selected optimally for the measuring task, and an evaluation and display unit. For carrying out the test, a small quantity of the liquid that is to be tested is introduced into the vessel, mixed with the reagents, agitated or, as appropriate, additionally heated. This produces a color reaction. The intensity of the color reaction characterizes the component in the liquid that is to be detected. The color intensity is determined by the evaluation and display unit and converted into a concentration of the sought substance. The disadvantages with this type of liquid testing are the relatively complicated measurement procedure, which requires the user to have laboratory skills, and the high cost of the evaluation and display unit.
Paper-based, or plastic-based test strips are also prior art. In the case of the test strips, certain chemical reagents, specific to the substance that is to be detected, are applied to an end of the paper. The test strips are immersed in the liquid that is to be tested. If a not inconsiderable content of the sought substance is contained in the liquid, it produces, with the reagents on the paper, a color reaction, of which the intensity is a measure of the concentration of the sought substance in the liquid. There is no need to take a sample; the test strip can be immersed directly in the liquid that is to be tested. The pH test sticks constitute a very well known example of this type of liquid testing. The disadvantage with the test sticks is that only straightforward ion-selective reactions can be realized. Biological parameters such as the biological oxygen demand or more complex chemical parameters such as the chemical oxygen demand of a liquid cannot be determined therewith.
Also small compact analysis systems with a volume of approximately 50 cm3 are prior art. The liquid that is to be tested is introduced with a pipette. The analysis system is then disposed in a separate external evaluation and display unit. This unit contains apparatuses in the form of mechanical and/or electroosmotic pumps, with the aid of which the liquid samples can be moved through tunnels in the analysis system. Moreover, the unit provides the auxiliary energy for detecting the sought components. Electrochemical and/or visual detection methods are implemented in the evaluation. A considerable amount of auxiliary energy is required for this purpose. The disadvantage with this type of liquid testing is that an expensive and complicated external evaluation and display unit is required.
It is accordingly an object of the invention to provide a method of, and sensor for, testing liquids that overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and that makes it possible to test liquid more straightforwardly and, in addition, cost-effectively than has been the case hitherto.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of monitoring liquids. The method includes sampling a liquid containing constituents. The next step is dissolving a maximum amount of a reagent in the liquid. The next step is reacting the reagent with the constituents to produce a remaining amount of the reagent. The next step is visually detecting the remaining amount of the reagent. The next step is correlating the detected remaining amount of the reagent with a quantity of the constituents.
With the objects of the invention in view, there is also provided a sensor for monitoring liquids. The sensor includes a sheet-like structural element with an inlet opening, a sample-accommodating channel, a mechanical pump, a transporting capillary, a detection zone, an emptying channel, and an outlet opening.
The invention described hereinbelow overcomes the disadvantage of the prior-art configurations. It discloses a liquid sensor that is inexpensive to produce, is easy to use, is intended preferably for a single use, and does not require any external evaluation unit. The sensor makes possible, inter alia, a quick semi-quantitative analysis for determining the biological or the chemical oxygen demand of a liquid. It supplies application-specific information about the state of a liquid. Following the measurement, the sensor is disposed of. Possible fields of use of the invention are, for example, small, decentralized clarification plants without extensive instrumentation for monitoring the water quality. Even unskilled personnel can accomplish this monitoring by using the sensor according to the invention. It is also possible for the sensor to be used, for example, in the process control in drinks manufacturing.
The sensor is of the size of a credit card, it is not more than 5 mm in thickness and has a surface area of 5xc3x978 cm2. A straightforward mechanical pressure pump that is activated by a membrane being subjected to finger pressure transports the liquid sample. The liquid is then transported by capillary action through the interior of the sensor to an outlet opening. Provided within the sensor, at certain locations, are small deposits of reagents that dissolve in the liquid as the latter flows past and trigger the corresponding chemical detection reaction. Also disposed in the sensor are enzymes or catalysts that accelerate a certain chemical detection reaction. The detection reactions are selected such that the result is displayed visually by the change in color on color indicators. The changes in color can easily be seen with the naked eye without any exterior assistance being used. The duration of an analysis is from two to five minutes (2-5 min.).
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of, and sensor for, testing liquids, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.